Introduction to Sterility Testing of Pharmaceutical Products
Sterility testing of Pharmaceutical Products is a critical quality control procedure to ensure that pharmaceutical products intended to be sterile are free from viable microorganisms.
This testing is essential for products like injectables, ophthalmic preparations, and certain solids and liquids.
The procedures are largely harmonized across major pharmacopeias, including the Indian Pharmacopoeia (IP), British Pharmacopoeia (BP), and United States Pharmacopeia (USP), with minor variations.
General Principles
Objective: To confirm that a product is sterile and safe for patient use.
Test Methods: Two primary methods are employed:
a) Membrane Filtration Method
b) Direct Inoculation Method
1. Membrane Filtration Method
Applicability:
Preferred for filterable products like clear liquids and some soluble solids.
Procedure:
Filtration: Pass the test sample through a sterile membrane filter with a pore size not greater than 0.45 μm.
Rinsing: Wash the membrane with sterile diluent to remove inhibitory substances.
Incubation: Divide the membrane and place into two culture media:
Fluid Thioglycollate Medium (FTM): Incubate at 30–35°C for detecting anaerobic and some aerobic bacteria.
Soybean-Casein Digest Medium (SCDM) or Tryptic Soy Broth (TSB): Incubate at 20–25°C for fungi and aerobic bacteria.
Duration: Incubate for not less than 14 days.
Advantages:
Removes inhibitory substances.
Suitable for large sample volumes.
2. Direct Inoculation Method
Applicability:
Used when filtration is not feasible, such as with ointments, creams, and insoluble solids.
Illustration of Direct Inoculation Method
(Image is just for representation purpose may contain incorrect data)
Procedure:
Inoculation: Add a specified quantity of the test sample directly into each culture medium.
Volume Constraints: The sample volume should not exceed 10% of the medium volume to prevent dilution of nutrients.
Incubation: Same media and conditions as the membrane filtration method.
Duration: Incubate for not less than 14 days.
Considerations:
May require dilution or emulsification of the sample.
Careful handling to avoid contamination.
Product-Specific Considerations
1) Liquids
Aqueous Solutions: Typically tested via membrane filtration.
Oily or Viscous Liquids: May need emulsification with sterile polysorbate 80 or other suitable agents before filtration.
2) Solids
a) Soluble Solids:
Preparation: Dissolve in a suitable sterile diluent.
Testing: Proceed with membrane filtration.
b) Insoluble Solids:
Preparation: Suspend in sterile diluent.
Testing: Use direct inoculation.
3) Ophthalmic Products
Solutions and Suspensions: Membrane filtration is preferred.
a) Ointments and Gels:
Preparation: May require melting or dilution with sterile solvents.
Testing: Direct inoculation into media.
4) Other Sterile Products
Medical Devices: Rinsed with sterile fluid; the rinse fluid is then tested.
Aerosols and Gases: Collected aseptically and tested via appropriate methods.
Differences Among IP, BP, and USP
Sample Quantity: Minor variations may exist in the required sample volumes or quantities.
Interpretation and Retest Policies: Procedures for retesting after a failed test might differ slightly.
Specific Microorganisms for Controls: The pharmacopeias may specify different strains for the growth promotion test.